This invention relates to lawn mowers, and more particularly, a lawn mower cutter assembly.
Self propelled riding lawn mowers are well known in the art. Such mowers generally include a cutter assembly, an engine for driving the cutter assembly and the mower's drive wheels. Such riding mowers are also often provided with a conduit and blower assembly for conveying the clippings from the cutter assembly to a hopper. In some localities, the collection of grass clippings is prohibited because of limitations on dumping sites. As a result, grass clippings are not collected but are either mulched or discharged from a discharge opening which forms a part of the cutter deck.
In order to provide adequate cutting widths, commercial type lawn mowers are commonly provided with a plurality of cutter blades. One type of mower includes two cutter blades that rotate in opposite directions and discharge grass clippings through the center rear of the cutter deck. In order for the mower to execute a complete cut for each pass, it is necessary for the blades to be long enough to overlap in the center. This, in turn, requires that the blades be mechanically timed to prevent them from engaging. The usual method is to use a gear box for supporting rotating the individual blades. Gears control the timing of the blade rotation to prevent impact. Another method of controlling the blade rotation employs a cog belt and pulleys. In order to uncouple the cutter blade from the gear box or timing belt should the blade strike a heavy or immovable object such as a tree root, rock, pipe or the like, such mowers are commonly provided with shear bolts, which are intended to allow the blades to decouple from the gear box or drive system. In practice, shear bolts do not always work as intended. In such cases, the shock load is severe enough to damage the gear box resulting in an expensive repair. Even when the shear bolts do protect the gear box from damage, the shear bolts themselves must be replaced causing down time and inconvenience to the user.
One system which eliminates the requirement for overlapping blades is to use three cutters which are staggered as disclosed in U.S. Pat. No. 4,226,074. This permits the swath cut by the center blade to overlap those of the outer blades without the blades themselves overlapping. Such three-blade systems, however, are not wholly satisfactory because it is difficult to achieve both a center rear discharge for collecting clippings in a hopper and an optional side discharge when the clippings are not mulched or collected. The use of a center rear collection system insures that both sides of the cutter deck are clear to trim against walls, trees, fences and the like without requiring that the deck be wider than required. Prior art three-blade cutter systems generally employ a side discharge chute or a collection boot for delivering clippings to a catcher system. The side with the chute or boot typically extends ten to twelve inches from the end of the nearest cutter blade. This prevents grass from being cut in that area.